Recently, attention has been attracted to recycle technique owing to ecological problems and the like. Many recycling methods using molding processes are known, and most of the moldings obtained by the methods have to be formed, on the surface thereof, with a cover mark, or have to be decorated by some methods. However, all of these methods require a great facility investment and may be, in some cases, difficult in application to products of complicated profiles. Thus, there is no method, which is capable of meeting all requirements in the molding processes.
Re-pelletization is a method of once again reducing to molding materials. Plastic parts collected from the market are classified depending on the types of materials. Thereafter, matters with similar colors are, respectively, collected, followed by washing so as to remove dirt from the surfaces, subjecting to crushers for coarse powdering and to grinding machines for fine powdering, coloring for color re-matching or complementarily, and re-pelletization to obtain a re-pelletized material.
The problem involved in this method is that since the collected moldings are soiled, the washing step is initially required. The washing includes ones using a solvent and water. First, dirt is removed by use of an organic solvent such as an alcohol, and then water is used to completely remove dirt from remaining portions. Pouring water into a device at the stage using a crusher in most cases carries out the water-washing step. A great amount of water is used, involving a great deal of cost (a cost for water). Moreover, the treatment of wastewater entails much cost. If no attention is paid to the wastewater treatment, a new problem of public nuisance (ecological pollution) may be caused.
The collected plastic moldings usually have colors, which are different from one another, and classification is necessary for collecting moldings having the same or similar color. Plastics are faded in color in a long-term use by exposure to light particularly, UV light. Accordingly, if moldings of the same color are collected and merely re-pelletized, their original color is not restored. For the restoration of the original color, color re-matching or complementarily is necessary. This eventually needs a further cost for the color matching.
In the above method, a large-scale investment is necessary for washing machines for satisfactorily removing dirt and devices for color matching or complementarily. If washing or color re-matching or complementarily is insufficient, there arises the problem on foreign matters or mottle or color drift. Thus, the re-pelletization can not solve all the recycling problems in view of the material control and economy. Among these problems, the problem on washing and the problem of costs involved in the labor for color classification and in the color re-matching or complementarily can be solved by the following surface painting treatment.
The surface painting method is one, which is simple and is highly realistic for recycling. In this method, the plastic parts collected from the market are classified depending on the types of materials, after which they are washed, subjected to crushers for coarse and fine powdering, and re-pelletized to obtain re-pellet materials.
The problem involved in this method is that the collected moldings have colors which are different from one another, and the moldings become dirty and are faded by the action of UV light or the like. If they are crushed and re-pelletized as they are and the resultant re-pelletized material is used for molding, there arise the problems on the mottle•foreign matters.
In order to solve the mottle·foreign matter problems, a cover mark, i.e. a surface paint treatment is necessary. In this connection, however, the paint used for this purpose is made of a material different in type from that of a molding. More particularly, while the materials for moldings are composed of thermoplastic resins, the paints used for the surface painting treatment are mainly made of thermosetting resins such as melamine resins, urethane resins, acrylic resins, epoxy resins and the like. Under these circumstances, it is difficult for recycling to crush and re-pelletize, as they are, moldings, which have been subjected to surface coating without removing the paint film therefrom. This is because the thermoplastic resin, which is a constituent of a molding, and a thermosetting resin used as a constituent of the paint have no affinity for each other.
For this reason, when the paint made of a conventionally employed thermosetting resin is used, the recycling may be feasible by only one time (usually called first cycle or first turn). However, the recycling cannot be performed in a closed loop such as of a second time (a called second cycle or second turn), a third time (called a third cycle or third turn), and the like.
With respect to the treating method of coated moldings, many attempts for reuse of coated thermoplastic resin moldings have been made and proposed in Patent Applications. The methods set out in these applications can be broadly classified into a method of removing a paint film by a physical manner, a method of separation with solvents, a method of hydrolyzing a paint film, and a method wherein a molding is crushed and used as it is.
The method of physically removing a paint film is set forth, for example, in Japanese Laid-open Patent Application No. Hei 2-273207 wherein coated thermoplastic resin moldings are subjected to straight-hydraulic blasting by use of a soft abrasive to separate the paint film therefrom crushed and re-pelletized.
In Japanese Laid-open Patent Application Nos. Hei 6-8245 and 6-8246, there is set out a method wherein coated thermoplastic resin moldings are crushed and melted, followed by separation of the film through a fine mesh screen.
Japanese Laid-open Patent Application No. Hei 6-226742 describes a method wherein a paint film is heated by means of a gas burner to form a thin melt layer beneath the film, and separated by scraping the film off.
Japanese Laid-open Patent Application Nos. Hei 6-328444 to 328446 describes a method of film removal using stretching by rolling.
Japanese Laid-open Patent Application No. Hei 6-328442 sets out a method wherein a paint film is rubbed off by shot blasting, followed by coating again.
As a method of separation with solvents or a method of hydrolyzing a paint film, there are described, for example, in International Laid-open No. WO 93/01232 and Japanese Laid-open Patent Application Nos. Hei 6-55539 and 6-234123, method of hydrolyzing a film with water or a solvent to provide low molecular weight substances, and uniformly dispersing them in a matrix resin.
In Japanese Laid-open Patent Application Nos. Hei 5-228936, 5-337940 and 5-25570, it is stated that after a film is decomposed such as by hot water treatment or alkali contact treatment, moldings are melted, as they are, in a resin along with the film.
As a method of crushing resin moldings attached with a paint film thereon for use, as it is, Japanese Laid-open patent Application No. Hei 6-134757 proposes a method wherein coated resin moldings are crushed and extruded under melt mixing conditions while adding a shear force at a predetermined level or over to cut the film into pieces having a size of 500 μm or below.
Another method of crushing resin moldings having a paint film thereon is set out in Japanese Laid-open Patent Application No. 7-241848, in which a crushed product of a thermoplastic resin coated with a thermosetting paint is mixed with a thermoplastic matrix resin having a viscosity of 90 poises (g/cm·second) or over at 200° C., and the mixture is mixed and extruded. The paint film is stripped and separated into finer pieces by the shear force exerted in the course of division into the finer pieces, and dispersed in the matrix resin. Although the resultant mixed product can be used, as it is, as a molding material, it may be formulated in a fresh material of a similar type in appropriate amounts.
Japanese Laid-open Patent Application No. 8-34088 pertains to an arrangement including parts of electronic appliances and a sheet member attached thereto, both of which are constituted of thermoplastic resins miscible with each other and in which an adhesive used for the attachment of the sheet member is constituted of a thermoplastic resin miscible with both the parts and the sheet member.
The method set out in the Japanese Laid-open Patent Application No. 2-273207 not only is complicated in steps, but also has to introduce a washing step for abrasives in practice. Thus, the complicated procedure becomes more complicated with poor economy. The abrasive used for the blasting is stuck in the resin molding, with the attendant problem that a difficulty is involved in removing all the particles of the abrasive.
The methods of the Japanese Laid-open Patent Application Nos. Hei 6-8245 and Hei 6-8246 are not only complicated in steps, but also cause the screen to be clogged on several occasions, thus requiring a frequent exchange with fresh ones. Thus, an additional equipment investment is necessary, with poor economy. Moreover, this technique has the problem that the paint film is not actually separated in 100%, and how far the film is separated cannot be readily confirmed by a simple manner. If the film is incorporated in a resin, there arises the problem that physical•chemical characteristics (hereinafter referred to as “material physical properties” of the resin lower.
In the Japanese Laid-open Patent Application No. Hei 6-226742, thermoplastic resins are originated from organic matters and are combustible, with the danger of causing fires in this method. The additional step is necessary, thus being relatively poor in economy.
In the Japanese Laid-open Patent Application Nos. Hei 6-328444 to 328446, the step of removing a paint film is additional, with the need of an additional equipment investment, thus being poor in economy. As for the Japanese Laid-open Patent Application No. Hei 6-328442, where painting is performed again according to the method, very careful attention has to be paid to shot blasting conditions, and otherwise, the underlying layer would become roughened, with the attendant problem that a good painting surface cannot be expected after re-painting.
The Japanese Laid-open Patent Application No. Hei 6-134761 has the problem that the steps of the method are complicated, with poor economy.
The Japanese Laid-open Patent Application No. Hei 6-023748 has the problem on the treatment of waste water and is not good economy. Since the film is separated, decomposed and gasified, there may arise the problem on the treatment of exhaust gases in order to prevent contamination in working environments. If gases obtained by the gasification are inflammable, a measure for fire prevention is necessary.
In the International Laid-open No. WO 93/01232 and the Japanese Laid-open Patent Nos. Hei 6-55539 and 6-234123, the addition of an acid or alkali is necessary. To this end, the waste liquor therefor has to be treated, thus being not economical. The use of an acid or alkali worsens working environments, and such a working environment has to be improved such as by establishing good ventilation. This incurs a new equipment investment.
In the Japanese Laid-open Patent Application Nos. Hei 5-228936, 5-337940 and Hei 5-25570, the incorporation of a thermosetting resin for a paint in a thermoplastic resin of a molding eventually leads to a lowering of physical properties. When molding, coating and pelletizing operations are repeated several times, the amount of a paint film gradually increases along with an increase in ratio of the film, resulting in the lowering of material physical properties.
If, for example, a 15 μm thick paint film is applied onto a molding having thickness of 3 mm in one painting cycle, the film is incorporated in the thermoplastic resin in an amount of 0.5%. Eventually, the molding obtained after repetition, for example, of five recycles contains 2.5% of the film, calculated as 0.5%×5, i.e. the number of painting cycles or the number of recycles. Where 2.5% of the film is incorporated, it is inevitable that material physical properties lower.
In the Japanese the Japanese Laid-open Patent Application No. Hei 6-134757, it is stated that coated thermoplastic resin moldings are crushed and kneaded under melting conditions while adding not lower than a predetermined shear force thereto, under which physical properties of the material do not lower when the film pieces are incorporated. The incorporation of either a thermosetting resin of the film or a thermoplastic resin having no affinity in the thermoplastic resin for a molding actually leads to the lowering of material physical properties.
During the course of repeating molding, painting and pelletizing cycles several times, the amount and ratio of a film increases, and the material physical properties apparently lower. As illustrate before, if, for example, a 15 μm thick paint film is applied onto a molding having thickness of 3 mm in one painting cycle, the film is incorporated in the thermoplastic resin in an amount of 0.5%. Eventually, the molding obtained after repetition, for example, of five recycles contains 2.5% of the film, calculated as 0.5%×5, i.e. the number of painting cycles or the number of recycles. Where 2.5% of the film having no affinity for the thermoplastic resin in the molding is incorporated, material physical properties inevitably lower.
Moreover, it is necessary that the film be crushed without separation and mixed under melting conditions while adding thereto a shear force at a predetermined level or over. To this end, a twin-screw extruder having a high shear force is used, and the extrusion has to be performed at revolutions of the screw as high as 450 r.p.m. This is the problem resulting from the fact that the film has no affinity for the thermoplastic resin of moldings.
In the course of division into fine pieces by mixing and extruding the mixture of the crushed product of a thermoplastic resin attached with a thermosetting resin film and a thermoplastic matrix resin having a viscosity of 90 poises (g/cm·second) or over at 200° C. the film is separated, broken and divided into fine pieces by the shear force exerted thereon. The resultant mixed product, in which the fine pieces are dispersed in the matrix resin, is molded. Since the finely divided pieces of the thermosetting film are miscible with the thermoplastic matrix resin, there arises the problem that sufficient strength cannot be obtained.
The sheet member and the adhesive attached on a portion of the parts of the electronic appliance are made of a thermoplastic resin miscible with the material of the parts and the adhesive attached to the sheet member is made of a thermoplastic resin miscible with the parts and the sheet member. Since the sheet member is bonded to the parts via the adhesive, there arises the problems that the attachment of the sheet member on the portion of the parts is limited to not larger than 20% of the total surface area of the parts, and the sheet member cannot be bonded to the entire surface of the parts and recycled.
The present invention contemplates to solve those problems stated hereinabove.